1) Field of the Invention
This invention relates generally to design and fabrication of metal lines and more particularly to fabrication of slots in metal lines for semiconductor devices.
2) Description of the Prior Art
The downward scaling of feature sizes in very large scale integration (VLSI) fabrication has resulted in the transition of the interconnect technology from Aluminum (Al) to Copper (Cu) for faster device performance. Owing to the differences between Al and Cu process, studies on the reliability performance such as electromigration (EM) between Al and Cu interconnects had since rose in importance. Less attention has been focused on the study of stress-induced voiding in Cu interconnects because of its favorable properties such as lower mobility and similar intrinsic stress level as compared to Al interconnects. However, this assumption has been illustrated to be opportunistic because of copper's strong dependency on process and structure.
Relevant patent and technical literature are shown below.
U.S. Pat. No. 6,528,883—Dunham, et al.—shows Shapes-based migration of aluminum designs to copper damascene. An interconnect structure for use in semiconductor devices which interconnects a plurality of dissimilar metal wiring layers, which are connected vias, by incorporating shaped voids in the metal layers.
U.S. Pat. No. 5,959,360 Fu—shows an interconnect structure employing equivalent resistance paths to improve electromigration resistance.
US 20030228714 A1—Smith et al. Dummy fill for integrated circuits—The described methods use process variation and electrical impact to direct the insertion of dummy fill into an integrated circuit.
U.S. Pat. No. 6,391,766—Wang, et al. shows a method of making a slot via filled dual damascene structure with middle stop layer.
U.S. Pat. No. 6,489,684 Chen, et al. shows a reduction of electromigration in dual damascene connector. Local back-diffusion sources serve to increase back pressure on the metallic ions that makes up the wire, thereby reversing the trend towards electromigration. These sources are located close to the vias in question and may take the form of discrete local areas where the wiring is wider or they may be introduced in the form of dummy vias.
U.S. Pat. No. 5,696,030—Cronin Integrated circuit contacts having improved electromigration characteristics and fabrication methods therefor. Increased cross-sectional contact sections are employed, with conducting studs in contact therewith.